The main purpose of this investigation is to study the effects of prolactin, estrogen and progesterone upon tumor growth and biochemical events. Established mammary cell lines of human or animal origin will be utilized for these studies. Once the effects of a single hormone are known, the interaction of these three hormones will be studied in order to elucidate the mechanism of hormonal action and interaction. In particular, the hormonal effects on the cellular concentrations of receptors, their translocation and nuclear events in gene regulation will be investigated. This investigation is of paramount importance not only in elucidating the fundamental principles governing the mechanism of hormonal action and interaction in normal and neoplastic tissues, but also will provide pertinent information in our understanding of hormonal dependence and independence in mammary cancers. Practical application for prognostication, early detection and treatment of this disease are implicated.